Use of casings in the food processing industry is well known. One segment of this industry uses casings in the production of food products involving whole muscles or large chunks of meat. An example would be smoked ham wherein the whole ham is stuffed into a casing for the smoking operation. Another example is a so called chunk-and-formed product where large meat chunks are combined for stuffing into a casing. For these types of food products, it is desirable that the casing have a plurality of vent openings in order to enhance or facilitate the expulsion of air from the casing as the large meat mass is stuffed into the casing, and to enhance or facilitate the draining of liquids such as water, meat juices and the like formed during or after processing.
A common stuffing method for producing these types of food products involves the use of flattened casing on reels and the stuffing apparatus as described, for example, U.S. Pat. No. 4,696,079. In this apparatus, a measured length of casing is pulled from the reel. The end of the casing is opened and a meat mass is rammed into the open casing. The open end is gathered and clipped to close it. Then the casing on the opposite side of the meat mass is gathered and the casing is pulled back from the clip closure so the casing wall is drawn up tightly around the meat mass thereby expelling entrapped air from between the casing and the meat mass. A second clip is applied to close a second end of the casing and then the casing is cut to separate the encased food product from the reel.
The speed and force of drawing the casing tight about the meat mass necessitates a perforated casing to facilitate the venting of air and excess liquids which may be squeezed from the meat mass as the casing tightens around it. Thereafter, during processing such as by cooking or smoking, additional gases and juices are released which are vented and drained from the casing through the perforations.
The most common method of providing the casing with vent holes is to flatten the casing and then prick through both plies of the flattened casing with sharp, pointed needles. If the casing is pricked from above, the perforations created will have inwardly disposed flaps in the upper ply of casing and outwardly disposed flaps in the bottom ply of the casing. The use of pointed needles also makes the vent flaps in the upper ply slightly larger than those in the bottom ply and all perforations may have somewhat jagged edges.
Due to the non-uniform configuration and size of the vent openings in the upper and lower plies, the venting of air, water and meat juices is not uniform about the circumference of the casing. The non-uniform venting also is the result of the closing of the inwardly disposed flaps during stuffing. This is because the pressure and meat mass tend to force these flaps outward so as to close off the vent openings. On the other side of the casing, the internal casing pressure forces the outwardly disposed flaps to remain open.
A further drawback of this casing is that the flaps produced by needle piercing are somewhat jagged and these jagged edges provide points of stress concentration where tearing can initiate when the casing is drawn tight about the meat mass. It also is possible for moving elements of the stuffing apparatus to snag on these flaps and initiate a tear or other casing failure.
Various efforts have been made to improve perforated casing. For example, U.S. Pat. No. 3,779,285 discloses use of a flat faced punch to make the vent opening. The punch is on a roller which interfaces with a backup roll having a resilient surface. As the punch presses the casing into the resilient surface, it tears a slug of casing from the upper and lower plies of casing and deposits them in the resilient surface of the backup roll. Since the backup surface is resilient, the lower ply still exhibited an outwardly flared edge caused by the passage of the punch. These flared edges still provide snag points and areas of stress concentration where tears can initiate. Moreover, venting still is not uniform around the casing perimeter and the backup roll has a relatively short life due to the constant contact with the punches.
Other attempts have been made to provide an improved perforated casing by using knife points. However, slits produced with knife points are not entirely satisfactory.
One drawback with prior art methods using pin or knife points to form the vents, or using punches against a resilient backup roll to knock slugs from the casing is that care had to be taken to avoid damaging the folded edge of the laid flat casing. This is because a sharp pin, knife point or punch which nicked the casing edge tended to produce a more ragged perforation in this area so the casing was more susceptible to tearing when drawn up tight against the meat mass. For this reason, care was taken to insure that the perforating apparatus did not operate out to or beyond the folded edge of the laid flat casing. This required a change in the set up of the apparatus for each different flat width of casing.
Accordingly, there is a need for perforated casing having improved venting properties and for methods and apparatus for making such a casing.